Flexible transferable vortex laser device for generating vortex laser and preparation method of flexible transferable vortex laser device

Abstract

The invention discloses a flexible transferable vortex laser device for generating vortex laser and a preparation method thereof, a two-dimensional grating periodic structure is obtained by using a double-beam interference exposure technology, and a mixed solution of a polymer material MDMO-PPV and a toluene solution is selected as a gain material to prepare the vortex laser device. And soaking the prepared device in a developing agent to remove all the photoresist on the glass substrate. Therefore, a flexible transferable vortex laser device is obtained, and wider application of vortex beams in life and production is promoted.

Description

Technical Field

[0001] The invention relates to the field of generating vortex lasers, and in particular to a method for preparing a concise, efficient, flexible and transferable vortex laser device. Background Art

[0002] Vortex beams are structured beams with orbital angular momentum carried by spiral wavefronts. They are widely used in optical data transmission, optical tweezers, quantum entanglement, super-resolution imaging and other fields. How to generate vortex beams with good performance is of great significance to these advanced applications. From the initial use of spiral phase plates to directly control the amplitude or phase of the light field using spatial light modulators to generate vortex beams. Later, it was proposed to use metasurfaces to improve the quality of vortex beams. Due to the low purity of spatial modes, this method of passively generating optical vortex beams through discrete components of bulky or planar elements will encounter low signal-to-noise ratio problems, which is critical and unavoidable in many applications. Therefore, the development of a simple and efficient method to generate vortex beams has become an urgent need in practical applications.

[0003] To solve this problem, in recent years, researchers have proposed ways to actively generate vortex beams, such as generating vortex beams based on traditional laser cavities, and then developing vortex beams based on laser microcavities. The characteristics of the resonance cavity itself are not conducive to the preparation of flexible ultra-thin lasers when generating vortex beams based on whispering gallery microring cavities. Based on the continuum bound state vortex laser, the continuum bound state (BIC) mode has an ultra-high quality factor and can thus achieve the characteristics of low-threshold emission of vortex lasers, which has attracted widespread attention from researchers. However, in current related research, no flexible and transferable applications based on continuum bound state vortex lasers have been proposed.

[0004] Double-beam interference lithography is a technology that records the interference pattern composed of two coherent light waves on the photoresist recording layer. This interference pattern consists of a periodic sequence of fringes, which represent the maximum intensity and the minimum intensity respectively. During the lithography process after exposure, the photoresist pattern corresponding to this periodic intensity variation pattern appears. The technology used to make the grating is interference holography. The grating period is defined by the formula Λ=λ / 2sinθ, where Λ is the grating period, λ is the wavelength of the interference source, and θ is half of the angle between the two interference beams. When building the interference optical path, the grating period can be accurately controlled by controlling the size of the angle between the two interference beams. A two-dimensional photonic crystal grating structure can be obtained by double exposure with a rotation of 90°. BIC can be generated in a two-dimensional photonic crystal microcavity. Based on the characteristics of BIC itself, using a two-dimensional photonic crystal microcavity to generate a vortex beam is an efficient preparation method. This technology is low-cost, simple and easy to operate, and has a positive role in promoting the preparation of vortex laser devices. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a flexible transferable vortex laser device, which uses a simple and efficient preparation technology to enable the vortex laser to generate stable and extremely low-loss vortex laser under the excitation of a femtosecond laser.

[0006] The technical solution adopted to achieve the purpose of the present invention is:

[0007] A method for preparing a flexible transferable vortex laser device comprises the following steps:

[0008] Step 1: Clean the glass substrate (1.5 cm × 1.5 cm) twice in anhydrous ethanol using ultrasonic cleaning, each time for 30 minutes, and then dry it thoroughly;

[0009] Step 2: Spin-coat the photoresist (PR, AR-P3170) on the glass substrate at high speed, and perform heating treatment after spin coating to form a PR film;

[0010] Step 3: Use 360nm continuous laser to perform holographic exposure on the prepared sample, and use the constructed double-beam interference optical path to expose the sample twice. The first exposure is 20s, and after the exposure is completed, the sample is rotated 90° for the second exposure, and the exposure time is 20s.

[0011] Step 4: After the exposure, the sample was placed in a developer (AR-300-47, Allresistance, Strausberg, Germany) to dissolve the imprinted part. The development time was 15 s, and a DFB resonant cavity with a grating structure period of 400 nm was obtained.

[0012] Step 5: Fix the sample with the grating structure by heating. After the sample is cooled, the gain material is spin-coated at high speed, which is a mixed solution of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV, Sigma-Aldrich) and toluene solution with a concentration of 8.5 mg / ml, to form a gain film on the grating structure;

[0013] Step 6: Soak the prepared device in a developer for one hour to dissolve all the PR in the device. After the PR is dissolved, a gain film with a grating structure can be obtained;

[0014] Step 7: Use a PET substrate with a circular hole to pick up the film. After it is dried naturally, use a femtosecond laser to pump the gain film to obtain a donut-shaped vortex beam.

[0015] Step 8: Based on step 6, use a clean glass sheet or lens to pick up the film. After it is naturally dried, use a femtosecond laser to pump the gain film to obtain a donut-shaped vortex beam, thus proving the successful preparation of a flexible transferable vortex laser device.

[0016] In the above technical solution, in step 2, the PR spin coating condition is high-speed spinning at 2500 rpm for 30 seconds, and the heating condition is heating at 110° C. for 1 minute.

[0017] In the above technical solution, in step 3, the power of the 360nm continuous laser is controlled to be 700-800μW during exposure. The period used when building a dual-beam interference optical path is defined by the period Λ of the DFB cavity, Λ=λ / 2sinθ, θ refers to half of the angle between the two interfering beams (λ=360nm) (θ=26°).

[0018] In the above technical solution, in step 4, the DFB resonant cavity is made by exposing twice using a double-beam interference optical path, and the grating structure obtained after development is similar to a two-dimensional photonic crystal, which serves as a laser resonant cavity.

[0019] In the above technical solution, in step 5, the heating treatment condition is 110° heating for 1 minute, the gain material is prepared by mixing 8.5 mg of MDMO-PPV with 1 ml of toluene solution, and the concentration of the obtained mixed solution is 8.5 mg / ml. The spin coating condition of the gain material is high speed 2500 rpm spin coating for 30 seconds.

[0020] In the above technical solution, in step 6, the purpose of placing the prepared device in the developer is to remove all the PR on the upper layer of the glass substrate. When the PR is completely dissolved, the gain film with the grating structure will automatically fall off from the glass substrate and float on the surface of the developer. The ultra-thin flexible transferable laser device can be obtained by picking it up and drying it.

[0021] In the above technical solution, in step 7, when the femtosecond laser pumps the laser device, the repetition rate used is 1 kHz, the pumping energy is 90%, and the pumping power of the femtosecond laser after passing through the attenuation plate is 400-500 μW.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1) The preparation of the flexible transferable vortex laser device provided by the present invention has low preparation cost, simple and easy operation method and good repeatability. 2) The flexible transferable vortex laser device provided by the present invention can generate efficient and stable vortex laser under the pumping of femtosecond laser. And the device can be placed on different objects as needed, and can still achieve vortex laser emission under the pumping of laser, which enhances the wide application of vortex laser devices in life and production. 3) The flexible transferable vortex laser device provided by the present invention has excellent comprehensive performance and has important application value in the field of vortex laser generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Shown is a schematic diagram of the preparation process of flexible transferable vortex laser devices;

[0024] Figure 2 Shown is a scanning electron microscope image of the grating structure;

[0025] Figure 3 Shown are the emission spectrum and threshold of the vortex laser device under laser pumping;

[0026] (a) is the emission spectrum of the vortex laser device under laser pumping;

[0027] (b) is the threshold of the vortex laser device under laser pumping;

[0028] Figure 4 The figure shows the far-field distribution of the laser emitted by the vortex laser device recorded by a spot analyzer; DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific implementation cases described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] Implementation Case 1

[0031] A method for preparing a flexible transferable vortex laser device comprises the following steps:

[0032] Step 1: Clean the glass substrate (1.5 cm × 1.5 cm) twice in anhydrous ethanol using ultrasonic cleaning, each time for 30 minutes, and then dry it thoroughly;

[0033] Step 2: Use a pipette to take 35 μl of photoresist (PR, AR-P3170), spin-coat PR on a clean glass substrate at a speed of 2500 rpm for 30 seconds, and heat it on a heating table at 110 °C for 1 minute to form a PR film;

[0034] Step 3: Use a 360nm continuous laser to perform holographic exposure on the prepared sample, and the power is controlled to 700-800μW during exposure. The period used when building the dual-beam interference optical path is defined by the period Λ of the DFB cavity, Λ=λ / 2sinθ, θ refers to the angle (θ=26°) between the two interfering beams (λ=360nm). Expose the sample twice using the constructed dual-beam interference optical path. The first exposure is 20s. After the exposure, rotate the sample 90° for a second exposure, and the exposure time is 20s;

[0035] Step 4: After the exposure is completed, the sample is placed in a developer (AR-300-47, Allresistance, Strausberg, Germany) to dissolve the imprinted part. The development time is 15 s. The grating structure obtained after development is similar to a two-dimensional photonic crystal, and a DFB resonant cavity with a grating structure period of 400 nm can be obtained;

[0036] Step 5: Fix the sample with the grating structure by heating. The heating condition for the heating treatment using a heating table is heating at 110° for 1 minute. After the sample cools down, use a pipette to take 50μl of the gain material and spin coat it at a speed of 2500rpm for 30s. The gain material is a mixed solution of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene](MDMO-PPV, Sigma-Aldrich) and toluene solution, which is made by mixing 8.5mg of MDMO-PPV with 1ml of toluene solution. The concentration of the obtained mixed solution is 8.5mg / ml. Thus, a gain film is formed on the grating structure;

[0037] Step 6: Soak the prepared device in the developer for one hour to remove all the PR on the glass substrate. When all the PR is dissolved, the gain film with the grating structure will automatically fall off the glass substrate and float on the surface of the developer. Pick it up and dry it to obtain an ultra-thin flexible transferable laser device.

[0038] Step 7: Use a PET substrate with a circular hole to pick up the film and let it dry naturally. Pump the gain film with a femtosecond laser, with a repetition rate of 1kHz, a pump energy of 90%, and a pump power of 400-500μW after the femtosecond laser passes through the attenuator. A donut-shaped vortex beam can be obtained;

[0039] Step 8: Based on step 6, use a clean glass sheet or lens to pick up the film, wait for it to dry naturally, and then use a femtosecond laser to pump the gain film. The repetition rate used is 1kHz and the pumping energy is 90%. A donut-shaped vortex beam can be obtained, which proves the successful preparation of a flexible transferable vortex laser device.

[0040] Attached Figure 3 Figure (a) shows the emission spectrum of the vortex laser device under femtosecond laser pumping. There are two emission peaks near the wavelength of 610nm. These two peaks correspond to the two modes of the continuous domain bound state. As the pump intensity increases, the emission peak intensity corresponding to one of the modes becomes larger and larger, while the emission peak intensity of the other mode gradually stops increasing with the increase of the pump intensity. Finally, one of the modes wins the competition and is displayed as a laser emission peak with a corresponding wavelength of 610nm. Figure (b) shows the threshold of the tested vortex laser device under laser pumping, which is 8.3μJ / cm 2 Compared with the existing laser devices for generating vortex lasers, the present invention has a lower lasing threshold.

[0041] Attached Figure 4 The far-field distribution of the laser emitted by the vortex laser device is recorded by the spot analyzer. The vortex laser device can be pumped by femtosecond laser, and the following Figure 4 The hollow vortex beam shown. The device is peeled off to obtain a flexible and transferable gain film with a grating structure. The gain film is placed on a mirror, glass, contact lens or some other object, and pumped with a femtosecond laser, and vortex laser can still be emitted. This flexible and transferable vortex laser device greatly reduces the production cost and has a wide range of flexible applications.

[0042] The spectrum of the emitted vortex laser was measured using a full-band spectrometer, and it was found that two emission peaks appeared near the wavelength of 610nm, which was in good agreement with the results calculated using the finite element analysis software (COMSOL). This proved that the prepared vortex laser device was based on the vortex laser generated by BIC, thus successfully preparing a flexible and transferable vortex laser device.

Claims

1. A method for preparing a flexible transferable vortex laser device for generating vortex laser, characterized in that: The method comprises the following steps: Step 1: Clean a 1.5 cm × 1.5 cm glass substrate twice in anhydrous ethanol using ultrasonic cleaning, each time for 30 minutes, and then dry thoroughly; Step 2: Spin-coat the cleaned glass substrate with photoresist PR at high speed, where the photoresist PR is AR-P3170, and heat-treat the substrate after spin-coating to form a PR film; Step 3: Use a 360nm continuous laser to perform holographic exposure on the prepared PR film, and use the constructed double-beam interference optical path to perform two exposures; the first exposure is 20s, and after the exposure is completed, the PR film is rotated 90° for a second exposure, and the exposure time is 20s; Step 4: After the exposure is completed, the PR film is placed in the developer AR-300-47 to dissolve the imprinted part. The development time is 15 seconds to obtain a DFB resonant cavity with a grating structure period of 400nm, that is, a sample with a grating structure is obtained; Step 5: Fix the sample with the grating structure by heating; after the sample is cooled, high-speed spin coating of the gain material is a mixed solution of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV, Sigma-Aldrich) and toluene solution with a concentration of 8.5 mg / ml to form a gain film on the grating structure; and the prepared device is obtained; Step 6: Soak the prepared device in a developer for one hour to dissolve all the PR in the device; after the PR is completely dissolved, a gain film with a grating structure is obtained; Step 7: Use a PET substrate with a circular hole to pick up the film, wait for it to dry naturally, and then use a femtosecond laser to pump the gain film to obtain a donut-shaped vortex beam; Step 8: Based on step 6, use a clean glass sheet or lens to pick up the film, wait for it to dry naturally, and then use a femtosecond laser to pump the gain film to obtain a donut-shaped vortex beam, thereby proving the successful preparation of a flexible transferable vortex laser device.

2. The method for preparing a flexible transferable vortex laser device for generating vortex laser according to claim 1, characterized in that: In step 2, the PR spin coating condition is high speed 2500 rpm spin coating for 30 seconds, and the heating condition is heating at 110° C. for 1 minute.

3. The method for preparing a flexible transferable vortex laser device for generating vortex laser according to claim 1, characterized in that: In step 3, the power of the 360nm continuous laser is controlled to be 700-800μW during exposure; the period used when building the dual-beam interference optical path is defined by the period Λ of the DFB cavity, Λ=λ / 2sinθ, θ refers to the angle between the two interference beams; the wavelength of the interference beam λ=360nm, and the angle of the interference beam θ=26°.

4. The method for preparing a flexible transferable vortex laser device for generating vortex laser according to claim 1, characterized in that: In step 4, the DFB resonant cavity is made by exposing twice using a double-beam interference optical path, and the grating structure obtained after development is similar to a two-dimensional photonic crystal, which serves as a laser resonant cavity.

5. The preparation method according to claim 1, characterized in that: In step 5, the heating treatment condition is heating at 110° for 1 minute, and the gain material is prepared by mixing 8.5 mg of MDMO-PPV with 1 ml of toluene solution to obtain a mixed solution concentration of 8.5 mg / ml; the gain material spin coating condition is high-speed spinning at 2500 rpm for 30 seconds.

6. The method for preparing a flexible transferable vortex laser device for generating vortex laser according to claim 1, characterized in that: In step 6, the purpose of soaking the prepared device in the developer is to remove all the PR on the upper layer of the glass substrate; when the PR is completely dissolved, the gain film with the grating structure will automatically fall off from the glass substrate and float on the surface of the developer. It can be picked up and dried to obtain an ultra-thin, flexible and transferable laser device.

7. The method for preparing a flexible transferable vortex laser device for generating vortex laser according to claim 1, characterized in that: In step 7 and step 8, when the femtosecond laser pumps the laser device, the repetition rate used is 1 kHz, the pumping energy is 90%, and the pumping power of the femtosecond laser after passing through the attenuation plate is 400-500 μW.

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